The introduction of a turbocharger into an internal combustion engine equipped with a catalyst is known. The turbocharger is driven by the exhaust gas coming from the engine and compresses air to be supplied to the engine so as to supply the engine with an increased amount of oxygen which results in generation of more power. As a result, the turbocharger consumes heat from the exhaust gas.
On the one hand, the catalyst is disposed in the exhaust line of the engine at a position downstream of the turbocharger and is arranged there so as to absorb emissions of the exhaust gas. Such a catalyst may for example be an oxidation catalyst which for the reduction of NOx and the oxidation of HC and CO requires a certain temperature level for working reliably. This means, that a certain period of time is needed from the beginning of the start of the engine until the exhaust gas has provided enough heat to warm-up the catalyst.
However, since the turbocharger is arranged in the exhaust line upstream of the catalyst and reduces the temperature of the exhaust gas, the warming-up of the catalyst may be delayed resulting in an extended period of time in which the catalyst does not work properly and in which an exhaust gas having a higher level of emissions is discharged to the environment (cold-start emissions).
To cope with this problem it has been proposed to arrange a pre-catalyst at the upstream side of the turbocharger. This position provides the pre-catalyst with a faster light-off performance which results in a decrease of the cold-start emissions.
There is a need to provide an improved pre-catalyst for an internal combustion engine having a turbocharger.